Resistance for contact $A-A$

${R_{AA}} = \rho \frac{x}{{2x \times 4x}} = \frac{\rho }{{8x}}$

Similar for contacts $B-B$ and $C-C$ are respectively

${R_{BB}} = \rho .\frac{{2x}}{{x \times 4x}} = \frac{\rho }{{2x}} = \frac{{4\rho }}{{8x}}$
and ${R_{CC}} = \rho \frac{{4x}}{{x \times 2x}} = \frac{{2\rho }}{x} = \frac{{16\rho }}{{8x}}$

It is clear maximum resistance will be for contact $C-C$.